1. Field of the Invention
The present invention relates to methods for regenerating wafers and substrates which were used in electric and electronic products such as semiconductor devices, magnetic recording media and optical recording devices, and apparatuses for performing the regeneration methods. In particular, the present invention relates to a method for effectively regenerating process wafers, test wafers and dummy wafers which are produced in semiconductor device production processes and an apparatus useful for performing the regeneration method. Although the present invention is also applicable to substrates other than the wafers set forth above, the present invention will be illustrated with reference to a test wafer as a typical example hereinafter.
2. Description of the Related Art
In semiconductor production lines, many test wafers are used for monitoring film thicknesses at various steps, particle inspections, and as dummy wafers in heating units. These wafers after use are repeatedly regenerated and used by removing functional coating films adhered to the surfaces and end faces, followed by washing.
In a typical conventional regeneration method, the regeneration is performed by the following steps (1) to (8):
(1) A removal step of a functional coating film by etching or double-face lapping; PA1 (2) A removal step of a layer deformed by working by etching if necessary; PA1 (3) A washing step of the wafer after the removal step of the functional coating film; PA1 (4) A bonding step of a plurality of wafers on a high stiffness ceramic plate with wax; PA1 (5) A polishing step of a wafer surface in which a plurality of ceramic polishing plates are loaded into a single-face polishing machine with a large turn table and the wafer surface is polished while a polishing slurry is added to a pad provided with the polishing plate; PA1 (6) A peel off step of the wafer from the ceramic polishing plates; PA1 (7) A washing step of wax (bonding agent) on the back face of the wafer; and PA1 (8) A finishing washing step. PA1 (1) The surface after etching is extremely nonuniform because various films having different etching rates are complicatedly wired and laminated; PA1 (2) Satisfactory regeneration cannot be achieved due to the residual films which cannot be removed by etching; and PA1 (3) Removal of hard films by double-face lapping causes the deformed layer formed during working to embed into the deep inside of the substrate. PA1 (a) a step for sorting the used wafer or substrate according to the quality, structure or thickness of the functional coating film; PA1 (b) a step for removing the functional coating film, while in a state of holding the used wafer or substrate, (i) by lapping the objective face of the used wafer or substrate with a hard metal-bonded whetstone while applying an electrochemical in-process dressing, (ii) by polishing the objective face while dropping a fine-particle polishing slurry between a polishing plate provided with a pad and the functional coating film, or (iii) by electrolyzing the functional coating film on the objective face placed opposite to an electrode face in an electrolyte solution at a predetermined voltage; PA1 (c) a step for mechanically removing the functional coating film adhered to the end face at an adequate stage; and PA1 (d) a step for washing and drying the used wafer or substrate after removal of the functional coating film. PA1 (1) a functional coating film removal unit for removing the functional coating film formed on the used wafer or substrate; PA1 (2) an end coating film removal unit for removing the functional coating film adhered to the end face of the used wafer or substrate; and PA1 (3) a surface washing unit for washing the treated face of the used wafer or substrate after removal of the functional coating film.
The double-face lapping of the step (1) is applied to remove hard films or complicated or multilayer films which cannot be removed by etching. FIG. 1 is a flow chart which illustrates the regeneration process set forth above.
Conventional test wafers were prepared for production of semiconductor devices having low levels of integration and relatively simple coating film structures. These films mainly consist of oxide films, polysilicon films, and aluminum films, and have simple structures consisting of at most 2 or 3 layers. Thus, the conventional regeneration process set forth above can satisfactorily respond to these wafers.
In recent years, levels of integration of semiconductor devices are significantly increasing due to extremely fine production processes. At the same time, various kinds of coating films with complicated structures have been formed on test wafers. For example, various hard coating films composed of W, WSi, TiSi, Si.sub.3 N.sub.4, TiN or the like have been increasingly used with conventional oxide films, polysilicon films and aluminum films, and the coating films consist of two to five layers for memory functions, or four to ten layers for logic bias functions.
Such circumstances set forth above have revealed that conventional regeneration methods have the following drawbacks (1) through (3):
Thus, a large working allowance is required to achieve a reusable level of surface smoothness in conventional regeneration processes. In detail, a working allowance of 40 to 60 .mu.m is required every regeneration process by conventional etching or double-face lapping, thus the number of regeneration cycles is limited to at most two or three. Further, the regeneration processes are inefficient, that is, the extremely smooth surfaces of silicon test wafers, on which functional coating films with thicknesses of at most 0.5 .mu.m are formed, are roughened by film removal processes and finely smoothed again with a large working allowance.
In conventional finish polishing after the coating film removal, a 6- to 8-inch wafer is bonded with wax to a ceramic plate with an outer diameter of 400 to 500 mm, and four to five ceramic plates are loaded on a large single-face polishing machine to perform a batch polishing process. Such a batch polishing process generally comprises two steps of rough polishing and finish polishing as set forth in FIG. 1, or three steps of rough polishing, preliminary finish polishing and finish polishing.
In these polishing steps, the wafer is uniformly bonded to a ceramic plate then peeled off from the plate. Thus, a large amount of equipment such as a wax mounter and a wax demounter must be provided, and a large amount of facility investment is required, even for the step of bonding the wafer to the ceramic plate.
Another regeneration method is also known, in which a wafer fitted on a glass-fiber reinforced template is polished. Since the template and wafer are fixed to each other in this method, a fraction of slurry may reach the back face of the wafer resulting in contamination, or the pad may crash due to separation of the wafer from the template during polishing.